Material Design was developed by Google and is a design language used for Android devices. The idea, according to Matias Duarte Vice President of Design for Google, is to provide a design language which mimics the feel of pen and paper. Material design offers the user physical edges and surfaces to work with. Seams and shadows gives context to what parts of a digital design can be touched.
Google Material Design is inspired by the properties of material in the physical world. Google states that GUI objects should feel like things in the real world. So to achieve this, the GUI is built as a three-dimensional space using layers and shadows. Movements are inspired by how objects behave in the physical world. The way that Material Design imitates the physical world should not be confused with Skeuomorphism, where GUI objects are designed to look like objects from the physical world. Rather than looking at different cultural objects, Material Design looks at the more basic, natural attributes of the physical world and what we expect from it, and tries to mimic those attributes.
In Material Design, as well as most other GUIs, objects ease in and out when they move from one place to another on the GUI. This gives the user a clear idea of what is happening to a GUI object, and it mimics the fact that objects in the physical world always move in an unobstructed path. They do not disappear and reappear somewhere else. In the physical world, objects also move along a nonlinear curve where they accelerate and decelerate at the beginning and end of movements. Easing makes the movement look more natural.
In Material Design, objects respond to touch input by moving, either up or down, on the z-axis to simulate pressure or on the x/y-axis. This mirrors the real-world actions of pressing and swiping, respectively. GUI objects also move when they touch other GUI objects like when the user places an object in the middle of a list of objects, the surrounding objects move to the side. Similarly, in the physical world, objects move when pushed by an outside force. Think of a bin full of balls at a sports store and what happens if you pick one up and drop it back in.
The Material Design guidelines state that GUI objects should move along a curve when moved diagonally up or down. Objects should also move faster when moving from the top to the bottom of the GUI than when moving from the bottom to the top. This imitates the effect that gravity has on movements in the physical world.
GUI animations work well when we design them to mimic not just the laws of physics but also of the physical world. Research has shown that we already have clear expectations from the time we are infants as to how objects should behave. Objects conform to laws. They exist when hidden. They can't move without help. They can't disappear and reappear somewhere else. They have to knock against one another to move each other. They fall from mid-air. When movements in GUIs behave according to our expectations, users can apply the same expectations to interact with the GUI.